The conventional sprinkler comprises a handle, a nozzle, and an extension pipe located between the handle and the nozzle. The extension pipe is provided with an adjustment device for adjusting the length of the extension pipe. The extension pipe is formed of an outer tube and an inner tube slidably fitted into the outer tube. The adjustment device comprises female threads, male threads, and a plurality of elastic retaining pieces which are arranged circularly at intervals. The elastic retaining pieces are intended to locate the inner tube. However, the elastic retaining pieces are ineffective in locating the inner tube.